Changes between Version 29 and Version 30 of GeneralImplementationConcept

Timestamp:

May 30, 2025, 6:15:14 PM (2 days ago)

Author:

lnerger

Comment:

--

GeneralImplementationConcept

@@ -37 +37 @@
 == Online and offline assimilation systems ==
 
-There are two possibilities to build a data assimilation system as sketched in Figure 2:
+There are two possibilities to build a data assimilation system. Figure 2 sketches how these are realized with PDAF:
  1. '''Online mode:''' [[BR]] In the online mode, calls to subroutines for the data assimilation are inserted into the model code. Thesse routines call the PDAF core routines. A single data-assimilative model program is compiled. While running this single program, the necessary ensemble integrations and the actual assimilation are performed. The information transfer between the model and the data assimilation functions are performed in memory.
  1. '''Offline mode:''' [[BR]] In the offline mode, the model is executed separately from the assimilation program. The model write restart files, which are used as inputs for the assimilation program. After computing the analysis step with the DA method, the assimilation program writes new restart files for the model, which is then started to compute the next forecast phase. In Figure 1, the model on the bottom left side is replaced by the reading and writing of files.
 
 [[Image(//pics/DAextension_offline-online_V3.png)]]
-[[BR]]'''Figure 2:''' Left: offline-coupled DA system with separate programs for model and assimilation; right: online-coupled DA system using model extended by data assimilation functionality. 
+[[BR]]'''Figure 2:''' Left: offline-coupled DA system with separate programs for model and assimilation; right: online-coupled DA system using model extended by data assimilation functionality. The blue boxes shows functionality of the model, while the green boxes are subroutines executed for PDAF (the names are explained in the pages explaining the two modes. They are linked on the bottom of the page). 
 
 PDAF supports both the online and offline modes. The online mode is usually more efficient on parallel computers, since less files have to be written to disks and the model does not need to be restarted after the analysis step. However, the required programming is simpler for the offline more than the online mode, since no modification to the model source code is necessary.
@@ -51 +51 @@
  * The assimilation system for the online mode can make efficient use of a large number of processors by executing a single program containing the full assimilation system. In contrast, in the offline mode, separate programs for the forecasts and the assimilation have to be run, each of these use typically a smaller number of processors.
 
-Generally the user-provided program code for the analysis step is very similar for the online and offline modes. The difference is mainly that in the online mode, one can access model fields and model grid information from the model source code (if the model is programmed in Fortran, the information is usually accessible via Fortran modules) while in the offline mode one needs to read the model fields and grid information from files. One can implement these reading operations in a way that for the offline mode the reading routines are used in the initialization phase, while all other subroutines remain independent on how the model fields and gird information are obtained.
+The user-provided program code for the analysis step is, in general, very similar for the online and offline modes. The difference is mainly that in the online mode, one can access model fields and model grid information from the model source code (if the model is programmed in Fortran, the information is usually accessible via Fortran modules) while in the offline mode one needs to read the model fields and grid information from files. One can implement these reading operations in a way that for the offline mode the reading routines are used in the initialization phase, while all other subroutines remain independent on how the model fields and gird information are obtained.
 
 The implementation concepts of the online and offline modes of PDAF are further described on separate pages: